System and method for firing a biofuel

ABSTRACT

A method of firing a biofuel is provided. The method includes: introducing the biofuel into a combustion chamber having a first stage and a second stage; combusting the biofuel in a suspended state while flowing from the first stage to the second stage; and introducing a first air stream and a second air stream into the combustion chamber at the first stage and at the second stage, respectively, to facilitate combustion of the biofuel.

BACKGROUND Technical Field

Embodiments of the invention relate generally to energy production, andmore specifically, to a system and method for firing a biofuel.

Discussion Of Art

As demand for renewable energy sources continues to grow, biofuels areincreasingly used in the production of energy. In particular, manyelectrical power plants, also referred to hereinafter simply as “powerplants,” burn biofuels to produce steam, which in turn powers a steamturbine generator. In many such power plants, the biofuel is burned on astoker grate within a combustion chamber. Burning biofuel on a stokergrate, however, can potentially create a relatively unpredictable and/oruncontrolled combustion reaction for a given amount of biofuel. Theterms “predictable” and “unpredictable,” as used herein with respect toa combustion reaction, refer to the likelihood that the combustionreaction will follow a predicted/calculated rate and/or stoichiometry.Typically, the more unpredictable/predictable a combustion reaction, theharder/easier it is to control the stoichiometry of the combustionreaction, and the greater/lesser the amount of mono-nitrogen oxides(“NOx”) produced from the combustion reaction. Accordingly, stoker gratebased power plants, which as stated above tend to create unpredictablecombustion reactions, generally create high amounts of NOx.

As NOx has been determined to contribute to the formation of acid rain,many governments have defined NOx emission limits for biofuel burningpower plants. In order to meet such NOx emission limits, many biofuelburning power plants employ both selective non-catalytic reducers(“SNCRs”) and selective catalytic reducers (“SCRs”). SNCRs and SCRs,however, are resource intensive and expensive to operate. Moreover, manySNCRs rely on ammonia (“NH3”) injection into an emitted flue gas for NOxreduction. Using NH3 to reduce NOx under the wrong temperatureconditions, however, risks NOx formation and/or NH3 slip in the emittedflue gas.

What is needed, therefore, is an improved system and method for firing abiofuel.

BRIEF DESCRIPTION

In an embodiment, a method of firing a biofuel is provided. The methodincludes: introducing the biofuel into a combustion chamber having afirst stage and a second stage; combusting the biofuel in a suspendedstate while flowing from the first stage to the second stage; andintroducing a first air stream and a second air stream into thecombustion chamber at the first stage and at the second stage,respectively, to facilitate combustion of the biofuel.

In another embodiment, a system for firing a biofuel is provided. Thesystem includes a combustion chamber having a first stage and a secondstage. The combustion chamber is operative to provide for combustion ofthe biofuel in a suspended state while flowing from the first stage tothe second stage. The combustion chamber further has a first injectorand a second injector operative to introduce a first air stream and asecond air stream into the combustion chamber at the first stage and atthe second stage, respectively, to facilitate combustion of the biofuel.

In yet another embodiment, a non-transitory computer readable mediumstoring instructions is provided. The stored instructions are configuredto adapt a controller to: introduce a biofuel into a combustion chamberhaving a first stage and a second stage; combust the biofuel in asuspended state while flowing from the first stage to the second stage;and introduce a first air stream and a second air stream into thecombustion chamber at the first stage and at the second stage,respectively, to facilitate combustion of the biofuel.

DRAWINGS

The present invention will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 is a block diagram of a system for firing a biofuel, inaccordance with an embodiment of the invention;

FIG. 2 is a diagram of a combustion chamber of the system of FIG. 1, inaccordance with an embodiment of the invention; and

FIG. 3 is a cross-sectional view of a firing layer of the combustionchamber of FIG. 2, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Reference will be made below in detail to exemplary embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference characters usedthroughout the drawings refer to the same or like parts, withoutduplicative description.

As used herein, the terms “substantially,” “generally,” and “about”indicate conditions within reasonably achievable manufacturing andassembly tolerances, relative to ideal desired conditions suitable forachieving the functional purpose of a component or assembly. The term“real-time,” as used herein, means a level of processing responsivenessthat a user senses as sufficiently immediate or that enables theprocessor to keep up with an external process. As used herein,“electrically coupled,” “electrically connected,” and “electricalcommunication” mean that the referenced elements are directly orindirectly connected such that an electrical current, or othercommunication medium, may flow from one to the other. The connection mayinclude a direct conductive connection, i.e., without an interveningcapacitive, inductive or active element, an inductive connection, acapacitive connection, and/or any other suitable electrical connection.Intervening components may be present. As also used herein, the term“fluidly connected” means that the referenced elements are connectedsuch that a fluid (to include a liquid, gas, and/or plasma) may flowfrom one to the other. Accordingly, the terms “upstream” and“downstream,” as used herein, describe the position of the referencedelements with respect to a flow path of a fluid and/or gas flowingbetween and/or near the referenced elements. Further, the term “stream,”as used herein with respect to particles, means a continuous or nearcontinuous flow of particles. As also used herein, the term “heatingcontact” means that the referenced objects are in proximity of oneanother such that heat/thermal energy can transfer between them. Asfurther used herein, the terms “suspended state combustion” refers tothe process of combusting a fuel suspended in air.

Additionally, while the embodiments disclosed herein are primarilydescribed with respect to power plants, it is to be understood thatembodiments of the invention may be applicable to any apparatus and/ormethod that needs to limit and/or eliminate NOx emissions resulting fromthe combustion of a biofuel, e.g., an incinerator.

Referring now to FIG. 1, a system 10 for firing a biofuel (12, FIG. 2),e.g., bagasse, switchblade and/or other grasses, wood, peat, straw,and/or other suitable biofuels, in accordance with embodiments of theinvention is shown. The system 10 includes a combustion chamber 14, andmay further include a controller 16 having at least one processor 18 anda memory device 20, a mill 22, an SCR 24, and/or an exhaust stack 26. Aswill be appreciated, the system 10 may form part of a power plant 28where the combustion chamber 14 is incorporated into a boiler 30 whichproduces steam for the generation of electricity via a steam turbinegenerator 32.

As will be understood, the mill 22 is operative to receive and processthe biofuel 12 for combustion within the combustion chamber 14, i.e.,the mill 22 shreds, pulverizes, and/or otherwise conditions the biofuel12 for firing within the combustion chamber 14. For example, inembodiments, the mill 22 may process the biofuel 12 to particles sizesless than or equal to about 2 mm. In other embodiments, the mill 22 mayprocess the biofuel 12 to particles sizes less than or equal to about 1mm. The mill 22 may be a non-screened styled hammer mill integrated witha flash drying column disposed at the inlet of a beater wheel exhaustfan. The processed biofuel 12 is then transported/fed from the mill 22to the combustion chamber 14 via conduit 34.

The combustion chamber 14 is operative to receive and to facilitatecombustion of the biofuel 12, which results in the generation of heatand a flue gas. The flue gas may be sent from the combustion chamber 14to the SCR 24 via conduit 36. In embodiments where the combustionchamber 14 is integrated into the boiler 30, the heat from combustingthe biofuel 12 may be captured and used to generate steam, e.g., viawater walls in heating contact with the flue gas, which is then sent tothe steam turbine generator 32 via conduit 38.

The SCR 24 is operative to reduce NOx within the flue gas prior toemission of the flue gas into the atmosphere via conduit 40 and exhauststack 26.

Turning now to FIG. 2, the combustion chamber 14 has two or more stages42 and 44, and one or more wind boxes 46 and 48 each having a pluralityof nozzles/injectors 50, 52, and 54. While FIG. 2 depicts the stages 42and 44 as discrete and spaced apart, it will be understood that, inembodiments, the stages 42 and 44 may be continuous and flush with oneanother, i.e., the stages 42 and 44 may smoothly transition from one 42to the next 44. As shown in FIG. 2, a first set of wind boxes 46 havenozzles 50 and 52 that are operative to introduce the biofuel 12 and afirst air stream 56 into the first stage 42. As will be appreciated, thefirst air steam 56 may be generated from both primary and secondary airsupplies. For example, in embodiments, nozzles 50 may introduce thebiofuel 12 into the first stage 42 via primary air, while secondary airis introduced into the first stage 42 via nozzles 52. Particles of thebiofuel 12 may be introduced into the combustion chamber 14 via nozzles50 at a slip speed, with respect to primary air, of between about 0-100feet/second. As used herein, the term slip speed refers to thedifference in the velocity of the particles of the biofuel 12 and thevelocity of the primary air transporting the biofuel 12 via nozzles 50.In embodiments, 100% of the biofuel may be injected by the nozzles 50within the first stage 42.

As also shown in FIG. 2, the nozzles 50 and 52 may be arranged into oneor more firing layers 60, 62 and 64, i.e., groups of nozzles 50 and 52disposed at and/or near the same position along a vertical/longitudinalaxis 58 of the combustion chamber 14. For example, a first firing layer60 may include nozzles 50 that introduce the biofuel 12 and primary air,a second firing layer 62 may include nozzles 52 that introduce secondaryair, and a third firing layer 64 may include nozzles 50 that introducethe biofuel 12 and primary air. While the firing layers 60, 62, and 64are depicted herein as being uniform, i.e., each firing layer 60, 62,and 64 includes either nozzles 50, that introduce only primary air andthe biofuel, or nozzles 52, that introduce only secondary air, it willbe understood that, in embodiments, an individual firing layer 60, 62,and 64 may include both nozzles 50 and nozzles 52. Further, while FIG. 2shows three firing layers 60, 62, and 64 in the first stage 42, it willbe understood that embodiments of the invention may include any numberof firing layers in the first stage 42.

Upon introduction into the first stage 42, the biofuel 12 and first airstream 56 are ignited such that the biofuel 12 combusts while in asuspended state. As further shown in FIG. 2, the second stage 44 isdownstream of the first stage 42 with respect to the combusting biofuel12. Thus, due to convective forces generated by combusting the biofuel12, particles of the biofuel 12 rise, or otherwise move, within thecombustion chamber 14 as they undergo combustion such that they flowfrom the first stage 42 to the second stage 44. In other words, thecombusting biofuel 12 forms a fireball 66 that spans the vertical axis58 from the first 42 to the second 44 stage.

As further shown in FIG. 2, a second set of wind boxes 48 have nozzles54 that are operative to introduce a second air stream 68, e.g., closedcoupled over-fired air and/or separated over-fired air, into the secondstage 44. Accordingly, as used herein, the terms “staged air,” “airstaging,” “staged combustion,” and “staging the combustion” refer toabove described splitting of the air consumed by the combustion of thebiofuel 12 between the first 42 and second 44 stages via the first 56and the second 68 air streams. As will also be appreciated, nozzles 54may be arranged into one or more firing layers 70 and 72 similar tonozzles 50 and 52 and firing layers 60, 62, and 64.

Moving now to FIG. 3, a cross-sectional view of firing layer 60 isshown. As will be appreciated, in embodiments, the biofuel 12 may betangentially fired, i.e., the biofuel 12 is introduced into the firststage (42 in FIG. 2) via nozzles 50 at an angle Φ formed between thetrajectory of the primary air component of the first air stream 56, anda radial line 74 extending from the vertical axis 58 to the nozzles 50.In other words, the nozzles 50 inject the biofuel 12 via the primary aircomponent of the first air steam 56 tangentially to an imaginary circle66, representative of the fireball, that is centered on the verticalaxis 58. In certain aspects, the angle Φ may range from 2-10 degrees.While FIG. 3 depicts the nozzles 50 within the first firing layer 60 asdisposed within the corners of the combustion chamber 14, in otherembodiments, the nozzles 50 may be disposed at any point within thefiring layer 60 outside of the fireball 66. As will be understood, thenozzles (50, 52 and 54 in FIG. 2) of the other firing layers (62, 64,70, and 72 in FIG. 2) may be oriented in the same manner as the nozzles50 of first firing layer 60 shown in FIG. 3. Accordingly, upon leavingthe nozzles 50, the particles of the biofuel 12 follow a helix shapedflight path 76, e.g., a corkscrew, within the fireball 66 as they flowfrom the first stage 42 to the second stage 44. In other words,tangentially firing the biofuel 12 causes the fireball 66 to rotateabout the vertical axis 58.

Returning back to FIG. 2, as will be appreciated, the helix shapedflight path 76 provides for a more controlled combustion reaction forparticles of the biofuel 12 over traditional stoker grate firingmethods. In particular, the helix shaped flight path 76 causes the fluegas to circulate about the “eye”/center of the fireball 66, i.e., thevertical axis 58, which dilutes the oxygen concentration within thefireball 66, thereby retarding the combustion reaction and/ortemperature. Further, staging of the combustion reaction additionallyretards the combustion reaction and/or combustion temperature, whichalso increases the de-NOx performance of the combustion reaction. Aswill be appreciated, the aforementioned provides for better control overthe stoichiometry of the combustion reaction. In particular, the first56 and the second 68 airstreams can be adjusted to regulate thestoichiometry of the combustion reaction in a predictable manner so asto limit the generation of NOx.

Accordingly, the first air stream 56 may provide a greater than or equalamount of air consumed by the combustion reaction than does the secondair stream 68. For example, in embodiments, the first air stream 56 mayprovide about 50-70% of the air consumed by the combustion of thebiofuel 12, which in turn regulates the stoichiometry of the combustionreaction of the biofuel 12 in the first stage 42 to between about0.6-0.8. As will be understood, the second air stream 68 provides theremaining air consumed by combustion reaction, which in turn regulatesthe stoichiometry of the combustion reaction in the second stage 44 toless than or equal to about 1.2. As will be understood, regulating thestoichiometry of the first 42 and the second 44 stages via staging ofthe combustion reaction, i.e., staging of the introduction of the first56 and second 68 air streams, drives nitrogen (“N”) out of the biofuel12 to become molecular nitrogen (“N2”) within the first stage 42, asopposed to forming NOx as typically occurs in the unpredictablestoichiometric conditions associated with traditional stoker gratemethods. In other words, in embodiments, the nitrogenous species arereleased from the volatile matter of the biofuel 12 and subsequentlyreduced to N2 by hydrocarbon intermediates within the first stage 42.

Thus, in certain aspects of the invention, combusting the biofuel 12 mayresult in about 0.08 lb/MBtu of NOx prior to treatment of the flue gasby the SCR (24 in FIG. 1) and/or without the use of support fuel. Assuch, the SCR 24 may further reduce the NOx within the emitted flue gasto less than or equal to about 0.01 lb/MBtu without the use of an SNCR.

Finally, it is also to be understood that the system 10 may include thenecessary electronics, software, memory, storage, databases, firmware,logic/state machines, microprocessors, communication links, displays orother visual or audio user interfaces, printing devices, and any otherinput/output interfaces to perform the functions described herein and/orto achieve the results described herein, which may be executed inreal-time. For example, as stated above, the system 10 may include atleast one processor 18 and system memory/data storage structures 20 inthe form of a controller 16 that electrically communicates with one ormore of the components of the system 10. The memory may include randomaccess memory (“RAM”) and read-only memory (“ROM”). The at least oneprocessor may include one or more conventional microprocessors and oneor more supplementary co-processors such as math co-processors or thelike. The data storage structures discussed herein may include anappropriate combination of magnetic, optical and/or semiconductormemory, and may include, for example, RAM, ROM, flash drive, an opticaldisc such as a compact disc and/or a hard disk or drive.

Additionally, a software application that provides for control over oneor more of the various components of the system 10 may be read into amain memory of the at least one processor from a computer-readablemedium. The term “computer-readable medium,” as used herein, refers toany medium that provides or participates in providing instructions tothe at least one processor 18 (or any other processor of a devicedescribed herein) for execution. Such a medium may take many forms,including but not limited to, non-volatile media and volatile media.Non-volatile media include, for example, optical, magnetic, oropto-magnetic disks, such as memory. Volatile media include dynamicrandom access memory (“DRAM”), which typically constitutes the mainmemory. Common forms of computer-readable media include, for example, afloppy disk, a flexible disk, hard disk, magnetic tape, any othermagnetic medium, a CD-ROM, DVD, any other optical medium, a RAM, a PROM,an EPROM or EEPROM (electronically erasable programmable read-onlymemory), a FLASH-EEPROM, any other memory chip or cartridge, or anyother medium from which a computer can read.

While in embodiments, the execution of sequences of instructions in thesoftware application causes the at least one processor to perform themethods/processes described herein, hard-wired circuitry may be used inplace of, or in combination with, software instructions forimplementation of the methods/processes of the present invention.Therefore, embodiments of the present invention are not limited to anyspecific combination of hardware and/or software.

It is further to be understood that the above description is intended tobe illustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. Additionally, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope.

For example, in an embodiment, a method of firing a biofuel is provided.The method includes: introducing the biofuel into a combustion chamberhaving a first stage and a second stage; combusting the biofuel in asuspended state while flowing from the first stage to the second stage;and introducing a first air stream and a second air stream into thecombustion chamber at the first stage and at the second stage,respectively, to facilitate combustion of the biofuel. In certainembodiments, introducing the biofuel into a combustion chamber furtherincludes tangentially firing at least some of the biofuel at the firststage. In certain embodiments, the biofuel has a maximum particle sizeless than or equal to about 2 mm. In certain embodiments, the first airstream provides a greater than or equal amount of the air consumed bycombustion of the biofuel than the second air stream. In certainembodiments, the first air stream provides about 50-70% of the airconsumed by combustion of the biofuel. In certain embodiments,combusting the biofuel produces less than or equal to about 0.08 lb/MBtuof NOx. In certain embodiments, the biofuel is at least one of bagasse,wood, peat, straw, and grass.

Other embodiments provide for a system for firing a biofuel. The systemincludes a combustion chamber having a first stage and a second stage.The combustion chamber is operative to provide for combustion of thebiofuel in a suspended state while flowing from the first stage to thesecond stage. The combustion chamber further has a first injector and asecond injector operative to introduce a first air stream and a secondair stream into the combustion chamber at the first stage and at thesecond stage, respectively, to facilitate combustion of the biofuel. Incertain embodiments, first injector is operative to introduce at leastsome of the biofuel into the combustion chamber at the first stage viatangential firing. In certain embodiments, the system further includes amill operative to provide the biofuel to the combustion chamber at amaximum particle size less than or equal to about 2 mm. In certainembodiments, the first air stream provides a greater than or equalamount of the air consumed by combustion of the biofuel than the secondair stream. In certain embodiments, the first air stream provides about50-70% of the air consumed by combustion of the biofuel. In certainembodiments, the system further includes a selective catalytic reducerthat is operative to limit NOx emissions resulting from combustion ofthe biofuel to less than or equal to about 0.01 lb/MBtu. In certainembodiments, the biofuel is at least one of bagasse, wood, peat, straw,and grass.

Yet still other embodiments provide for a non-transitory computerreadable medium storing instructions. The stored instructions areconfigured to adapt a controller to: introduce a biofuel into acombustion chamber having a first stage and a second stage; combust thebiofuel in a suspended state while flowing from the first stage to thesecond stage; and introduce a first air stream and a second air streaminto the combustion chamber at the first stage and at the second stage,respectively, to facilitate combustion of the biofuel. In certainembodiments, at least some of the biofuel is introduced into thecombustion chamber at the first stage via tangential firing. In certainembodiments, the biofuel has a maximum particle size less than or equalto about 2 mm. In certain embodiments, the first air stream provides agreater than or equal amount of the air consumed by combustion of thebiofuel than the second air stream. In certain embodiments, the firstair stream provides about 50-70% of the air consumed by combustion ofthe biofuel. In certain embodiments, combustion of the biofuel producesless than or equal to about 0.08 lb/MBtu of NOx.

Accordingly, by combusting the biofuel in a suspended state and stagingthe introduction of air consumed by the combustion reaction, someembodiments of the invention generate significantly lower amounts of NOxthan traditional methods of firing biofuels, e.g., stoker grates. Inparticular, some embodiments of the invention are able to achieve NOxemissions as low as about 0.08 lb/MBtu without the use of an SCR, and aslow as about 0.01 lb/MBtu with an SCR unaccompanied by an SCNR. Byeliminating the need for an SCNR to reach about 0.01 lb/MBtu emittedNOx, some embodiments of the invention greatly reduce the operationalcosts of an encompassing power plant. Additionally, by achieving NOxemissions as low 0.08 lb/MBtu, the SCR of some embodiments of theinvention may be smaller than those typically used in traditionalbiofuel power plants.

Further, the tangential firing of the biofuel 12 in some embodimentscauses the combustion reaction to occur “globally,” i.e., uniformly,within the first stage 42. Thus, some embodiments provide for theignition and/or mixing of the biofuel 12 and first air stream 56, aswell as improved flame stability, without the need for localized, highturbulence injections of fuel and air.

While the dimensions and types of materials described herein areintended to define the parameters of the invention, they are by no meanslimiting and are exemplary embodiments. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. In the appended claims,the terms “including” and “in which” are used as the plain-Englishequivalents of the respective terms “comprising” and “wherein.”Moreover, in the following claims, terms such as “first,” “second,”“third,” “upper,” “lower,” “bottom,” “top,” etc. are used merely aslabels, and are not intended to impose numerical or positionalrequirements on their objects. Further, the limitations of the followingclaims are not written in means-plus-function format and are notintended to be interpreted as such, unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

This written description uses examples to disclose several embodimentsof the invention, including the best mode, and also to enable one ofordinary skill in the art to practice the embodiments of invention,including making and using any devices or systems and performing anyincorporated methods. The patentable scope of the invention is definedby the claims, and may include other examples that occur to one ofordinary skill in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty.

Since certain changes may be made in the above-described invention,without departing from the spirit and scope of the invention hereininvolved, it is intended that all of the subject matter of the abovedescription shown in the accompanying drawings shall be interpretedmerely as examples illustrating the inventive concept herein and shallnot be construed as limiting the invention.

What is claimed is:
 1. A method of firing a biofuel a comprising: introducing the biofuel into a combustion chamber having a first stage and a second stage; combusting the biofuel in a suspended state while flowing from the first stage to the second stage; and introducing a first air stream and a second air stream into the combustion chamber at the first stage and at the second stage, respectively, to facilitate combustion of the biofuel.
 2. The method of claim 1, wherein introducing the biofuel into a combustion chamber further comprises: tangentially firing at least some of the biofuel at the first stage.
 3. The method of claim 1, wherein the biofuel has a maximum particle size less than or equal to about 2 mm.
 4. The method of claim 1, wherein the first air stream provides a greater than or equal amount of the air consumed by combustion of the biofuel than the second air stream.
 5. The method of claim 4, wherein the first air stream provides about 50-70% of the air consumed by combustion of the biofuel.
 6. The method of claim 1, wherein combusting the biofuel produces less than or equal to about 0.08 lb/MBtu of NOx.
 7. The method of claim 1, wherein the biofuel is at least one of bagasse, wood, peat, straw, and grass.
 8. A system for firing a biofuel comprising: a combustion chamber having a first stage and a second stage and operative to provide for combustion of the biofuel in a suspended state while flowing from the first stage to the second stage; and wherein the combustion chamber further has a first injector and a second injector operative to introduce a first air stream and a second air stream into the combustion chamber at the first stage and at the second stage, respectively, to facilitate combustion of the biofuel.
 9. The system of claim 8, wherein the first injector is operative to introduce at least some of the biofuel into the combustion chamber at the first stage via tangential firing.
 10. The system of claim 8 further comprising: a mill operative to provide the biofuel to the combustion chamber at a maximum particle size less than or equal to about 2 mm.
 11. The system of claim 8, wherein the first air stream provides a greater than or equal amount of the air consumed by combustion of the biofuel than the second air stream.
 12. The system of claim 11, wherein the first air stream provides about 50-70% of the air consumed by combustion of the biofuel.
 13. The system of claim 8 further comprising: a selective catalytic reducer that is operative to limit NOx emissions resulting from combustion of the biofuel to less than or equal to about 0.01 lb/MBtu.
 14. The system of claim 8, wherein the biofuel is at least one of bagasse, wood, peat, straw, and grass.
 15. A non-transitory computer readable medium storing instructions configured to adapt a controller to: introduce a biofuel into a combustion chamber having a first stage and a second stage; combust the biofuel in a suspended state while flowing from the first stage to the second stage; and introduce a first air stream and a second air stream into the combustion chamber at the first stage and at the second stage, respectively, to facilitate combustion of the biofuel.
 16. The non-transitory computer readable medium of claim 15, wherein at least some of the biofuel is introduced into the combustion chamber at the first stage via tangential firing.
 17. The non-transitory computer readable medium of claim 15, wherein the biofuel has a maximum particle size less than or equal to about 2 mm.
 18. The non-transitory computer readable medium of claim 15, wherein the first air stream provides a greater than or equal amount of the air consumed by combustion of the biofuel than the second air stream.
 19. The non-transitory computer readable medium of claim 18, wherein the first air stream provides about 50-70% of the air consumed by combustion of the biofuel.
 20. The non-transitory computer readable medium of claim 15, wherein combustion of the biofuel produces less than or equal to about 0.08 lb/MBtu of NOx. 